This invention relates to a method for storing nuclear fuel, especially spent nuclear fuel that has been extracted from a nuclear reactor and is to be stored for a shorter or longer time, e.g. while waiting for reprocessing, destruction or transport to an ultimate storage. Moreover, the invention relates to a system for carrying the method into effect.
It is known to contain spent nuclear fuel in large storage containers of concrete; such containers may be in the shape of parallelepiped shaped or, more common, circular cylindrical reinforced upstanding concrete bodies having a height of about 6 m and a diameter of 2.5 to 3 m, for example. Examples of embodiments of such storage containers are shown in DE-35 15 871-A1 and WO96/21932. The fuel to be stored in the storage container is placed in a fuel vessel or receiver, made of steel or other suitable material, which is embedded in the concrete body.
When spent fuel is extracted from a nuclear reactor it is usually placed in a water pool near the reactor, often within the nuclear power station, where it is kept until it is transported to a reprocessing plant or to a storage site, such a an ultimate storage.
Primarily, the present invention is concerned with the step of the storage process which includes containment of the spent nuclear fuel in a storage container. In the context of the invention that step also may include transfer of the spent fuel from the reactor site or an intermediate-storage pool to the site of where the containment is effected, and also the method for the disposition of the storage container in a storage site following the containment operation.
In accordance with the invention there is provided a method for storing nuclear fuel in a storage container including a concrete body and a fuel receiver embedded in the concrete body, which method comprises the steps of: introducing the nuclear fuel into the fuel receiver; providing formwork for the concrete body and mounting the fuel receiver within the formwork; placing the formwork in an immersed position in a pool containing a body of water; placing concrete in the immersed formwork to form the concrete body; and removing the formwork with the concrete body formed therein from the pool.
These steps need not necessarily be carried out in the order in which they are mentioned.
In the method according to the invention, the containment of the nuclear fuel in the storage container is integrated in the making of the storage container. The making of the major part if the storage container, i.e. the concrete body, and thus the embedding of the fuel receiver in the concrete thus is performed in its entirety under water and preferably in a manner such that the fuel receiver will be jointlessly embedded in the concrete.
The invention offers a possibility of a rational and secure implementation of the entire process, including the transfer of the nuclear fuel to and into the fuel receiver. Throughout this process the fuel can be immersed in water at a safe depth.
In accordance with the invention there is also provided a system for implementation of the process, namely a system for manufacturing a storage container for nuclear fuel, especially spent nuclear fuel, and containment of the fuel in a fuel receiver in a concrete body forming part of the storage container, said system comprising: a water pool of a depth at least equal to the height of the storage container to be manufactured; facilities for assembling concrete formwork for the concrete body of the storage container; facilities for moving the formwork and the fuel receiver to the water pool; facilities for introducing the nuclear fuel in the fuel receiver; facilities for placing concrete in the formwork with the formwork immersed in water in the water pool to form the concrete body in the formwork; and facilities for removing the formwork and the concrete body formed therein from the water pool.
Preferably, the pool has at least two pool sections which can be interconnected, suitably through a water lock, namely a pool section in which the fuel is introduced into the fuel receiver and another pool section in which the placement of the concrete in the formwork is effected. The depth of the first pool section suitably is at least equal to the sum of the height of the storage container and the height of fuel units, such as fuel assemblies or fuel rod units, which hold the fuel and are introduced from above into the fuel receiver. This depth permits keeping the fuel units constantly immersed. Preferably, the depth is such that the fuel units need never come closer to the water surface than 2 to 3 m. After the fuel units have been introduced into the fuel receiver and the fuel receiver has been sealed, the formwork is moved to the other pool section where the placing of the concrete is carried out. This pool section may have a lesser depth than the first pool section, but the depth should be at least equal to the height of the storage container so that the entire storage container can be constantly immersed.
Preferably, an further pool section is provided which communicates with the first pool section, suitably through a water lock. In this further pool section the fuel units may be placed while waiting for their introduction into the fuel receiver. This further pool section should also be of such a depth that the fuel units may be constantly immersed in the water and preferably have their top parts at least 2 to 3 m below the water surface.